A world without roast beef: who wants that except McCartney and Stern?

Sir Paul McCartney arrives in Brussels today to recruit support for his ‘meat free Mondays' campaign. The argument seems so easy: cut down meat consumption, slaughter methane-belching cattle, and the planet will be saved.

But even if a world without roast beef was one in which we all wanted to live (please count me out), we need to think a little harder about what will really work to arrest global warming. Why are Mondays to be free of meat alone? After all, dairy cattle produce greenhouse gases as well as milk. Are we meant to become part-time vegetarians or vegans? And why single out meat? Asia's paddy fields emit the same amount of methane as their livestock industry. It seems doubtful that a campaign for rice free Tuesdays will be next.

A global deal to combat dangerous climate change in succession to Kyoto is critical. But successful action won't end with a new international agreement, whenever it is struck.

For a start, we'll need to maintain the public pressure that is driving governments to agree action. That means guarding against demands for behavioural changes so profound and unrealistic that they risk undermining public support for the steps we can and must take.

The call last month by the Government's former climate change adviser, Lord Stern, effectively to give up meat eating altogether could almost have been calculated to reduce public support for climate change action. In fact, the people's response, according to a subsequent opinion poll, was to deliver Stern a loud raspberry. But the reputational damage to a vitally important cause may have been more serious.

There are legitimate questions about how land should be used in future as the world's population grows and western patterns of consumption spread. But some activists are less interested in serious debate than in pulling their hair shirts onto the rest of us. In their red-green world, capitalism is abhorent and meat is murder. But the planet we want to save is surely a world of prosperous, free people, where wealth can be shared and opportunity is available to all.

Lifestyles and business practices will certainly have to change. But we need to pursue sustainable growth, not to reject the idea of growth itself. To deny wealth to developing nations or dictate their diet is a form of environmental colonialism.

Of course, agriculture, which accounts for 18 per cent of global emissions, must play its part in reducing greenhouse gases. British farming may account for just 7 per cent of emissions, but in developing countries, or those whose economies are heavily dependent on agriculture, the share can be far greater.

But much of our grassland can only be used to rear animals: we couldn't use our green hills to produce cereals, even if we wanted to. Getting rid of our livestock in favour of trees isn't the answer, either. It is right to worry about rainforests being destroyed to produce cheap cattle feed, but the way to deal with that is to find better ways to protect the forests and source feed sustainably.

It would be great to have more trees in Britain in the right places. But smothering our farmed uplands with conifers wouldn't just be aesthetically damaging - it would be incredibly short-sighted.

Within a few decades, rapid global population growth and climate change will collide to produce a food crunch. We will need modern and productive agricultures to provide global food security. We can't just produce more food regardless of the environmental cost - farming must be sustainable. But we can't give up on production, either.

In the words of New Zealand's Prime Minister, John Key, we need to meet "the twin challenge of ensuring food security while reducing emissions". His proposal to boost international research into mitigating cattle emissions is a practical step. Abolishing livestock isn't.

Sir Paul is right on one point: effective action to prevent global warming will depend on securing individual behavioural change. This can't only be about policy agreed by politicians. Global targets, fiscal frameworks and the right political leadership are all necessary, but they aren't sufficient.

A consensus that extends only to the political elite is no consensus at all. Without widespread public buy-in, the societal shift needed to de-carbonise our economies won't follow. To encourage this democratic engagement we must frame policy in a way that incentivises and rewards people to do the right things.

That means setting out an optimistic vision of the world we're trying to protect - what David Cameron has called the "good future", where green technologies create new wealth and employment; where we all enjoy and truly value the fruits of a cleaner, more beautiful environment, and where individuals and communities live within their environmental means.

Right now, a climate deal seems hard. Making the changes that follow will be even harder. We can't allow political agendas to undermine the chance of success. Ultimately, we'll only achieve a good future if people want to get there.